Scattering of Cu(1 0 0) image state electrons from single Cu adatoms and vacancies: A comparative study

A theoretical study of the electron dynamics in image potential states on Cu(1 0 0) surfaces with different types of defects (Cu adatoms and Cu vacancies) is presented for low defect density at the surface. A wave packet propagation approach is employed for the electron scattering calculations, where the defect induced potentials are obtained from an ab initio density functional study. Scattering of the image state electron by a defect induces inter-band and intra-band transitions leading, respectively, to the population decay and to the dephasing of the image states. Comparison of the respective effects of adatoms and vacancies shows that Cu adatoms are much more efficient in inducing population decay and dephasing of the image potential states. Present results for the case of Cu adatoms are compared with available time-resolved two-photon photoemission data.